This invention relates to a signal conversion method for color image copying in a machine employing a thermally developable photosensitive material, a thermal transfer image copier, a laser beam printer, or the like.
When an original color image is scanned and converted into electrical signals which are thereafter processed and used to control the scanning of a photosensitive material by a recording head to thereby copy or reproduce the image, the fidelity of the copy is of paramount importance. A problem in this regard, however, is that the photosensitive recording material has spectral absorption characteristics such that cyan (C), magenta (M) and yellow (Y) colors become superimposed on one another when the material is irradiated with red (R), green (G) and blue (B) light during the copying process, as shown in FIG. 2, which results in an improper and undesired mixture of the C, M and Y colors. In addition, the spectral sensitivities of R, G and B decomposition systems are also superimposed on one another to some degree during the initial reading or scanning of the colored image to be reproduced. Accordingly, the scanner output representing the cyan component of the image will invariably include undesired portions of the magenta and yellow components.
A method of compensating for the improper coloring phenomena described above is disclosed in Japanese Kokai No. 14572/85, but this does not involve any photosensitive material and only treats false coloring caused by the spectral sensitivity characteristics of the light sources used. Such a method is thus inapplicable to a color copier machine, and a need therefore exists for a color signal conversion method in which the decomposition errors generated in reading a colored image can also be compensated for.